In the past, there has been known a segmented seal that seals an annular gap between a rotating shaft and a housing. This segmented seal includes a seal ring made of carbon that is in intimate contact with a side wall face of an annular concave portion formed in the housing, is disposed to be slidable on an outer peripheral surface of the rotating shaft, and has a structure in which the seal ring is segmented into a plurality of segments in a circumferential direction thereof. As a method of making this seal ring non-rotatable with respect to the housing, there is known one in which a key groove is formed on an end face of the seal ring, and a key that is engaged with the key groove is secured to the housing.
In such a method, there is a problem that in accordance with the rotation, vibration and the like of the rotating shaft, wear progresses on an inner peripheral surface side (i.e., a rotating shaft side) of the key groove due to its sliding movement against the key as time passes, and hence a deterioration of the seal ring is caused.